Storage systems having a plurality of storage devices are used to store and manage large amounts of data generated in many places, the data being stored in the storage devices in a distributed (multiplexed) manner. As the range of applications and the amount of information have been increasing in recent years, a greater storage capacity, more reliable services, and reliability and security solutions are demanded. One known storage system performs a distributed failure recovery process in accordance with the level of risk of losing data and the degree of performance degradation at a failure (refer to Japanese Laid-open Patent Publication No. 07-261945, for example).
One known example of the storage system is an organic storage which duplicates or moves data in accordance with the judgment made by the storage system itself. A general organic storage allocates a logical volume, and the user accesses the logical volume. The logical volume is formed by a plurality of segments, and each segment is formed by two slices. The slice is a partition of a predetermined size, formed by dividing a disk space provided by a storage node. A segment is formed by slices contained in different storage nodes. The slices forming the segment are divided into two types: a primary slice and a secondary slice.
The primary slice and the secondary slice are allocated with little consideration given to the attributes of the individual storage nodes (years of use, operation time, operating environment, etc.). For example, a new node and an old node could be handled in the same way, regardless of years of use. Redundant data might be kept by old storage nodes even though the old storage nodes generally have a high risk of failure. Keeping redundant data in the old storage nodes will increase the risk of losing data because the two nodes could go wrong in the same period.